System and method for optimizing efficiency and power output from a vanadium redox battery energy storage system

ABSTRACT

An energy storage system includes a vanadium redox battery that interfaces with a control system to optimize performance and efficiency. The control system calculates optimal pump speeds, electrolyte temperature ranges, and charge and discharge rates. The control system instructs the vanadium redox battery to operate in accordance with the prescribed parameters. The control system further calculates optimal temperature ranges and charge and discharge rates for the vanadium redox battery.

RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 11/032,280 filed Jan. 10, 2005, entitled “Systemand Method for Optimizing Efficiency and Power Output from a VanadiumRedox Battery Energy Storage System,” which claims the benefit of U.S.Provisional Application No. 60/536,662 filed on Jan. 15, 2004, andentitled “System and Method for Optimizing Efficiency and Power Outputfrom a Vanadium Redox Battery Energy Storage System” and to U.S.Provisional Application No. 60/541,534 filed on Feb. 3, 2004, andentitled “System and Method for Optimizing Efficiency and Power Outputfrom a Vanadium Redox Battery Energy Storage System,” all of which areherein incorporated by reference in their entireties.

TECHNICAL FIELD

This invention relates to vanadium redox battery energy storage systemsand associated automated control systems to enhance performance.

BACKGROUND OF THE INVENTION

Domestic and industrial electric power is generally provided by thermal,hydroelectric, and nuclear power plants. New developments inhydroelectric power plants are capable of responding rapidly to powerconsumption fluctuations, and their outputs are generally controlled torespond to changes in power requirements. However, the number ofhydroelectric power plants that can be built is limited to the number ofprospective sites. Thermal and nuclear power plants are typicallyrunning at maximum or near maximum capacity. Excess power generated bythese plants can be stored via pump-up storage power plants, but theserequire critical topographical conditions, and therefore, the number ofprospective sites is determined by the available terrain.

New technological innovations and ever increasing demands in electricalconsumption have made solar and wind power plants a viable option.Energy storage systems, such as rechargeable batteries, are an essentialrequirement for remote power systems that are supplied by wind turbinegenerators or photovoltaic arrays. Energy storage systems are furtherneeded to enable energy arbitrage for selling and buying power duringoff peak conditions.

Vanadium redox energy storage systems have received very favorableattention, as they promise to be inexpensive and possess many featuresthat provide for long life, flexible design, high reliability, and lowoperation and maintenance costs. A vanadium redox energy storage systeminclude cells holding anolyte and catholyte solutions separated by amembrane.

The vanadium redox energy storage system relies on a pumping flow systemto pass the anolyte and catholyte solutions through the cells. Inoperating a vanadium redox energy storage system, flow rates, internaltemperatures, pressure, charging and discharging times are all factorsthat influence power output. Thus, it would be an advancement in the artto provide a system and method for optimizing the efficiency of avanadium redox energy storage system.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the invention briefly described abovewill be rendered by reference to the appended drawings. Understandingthat these drawings only provide information concerning typicalembodiments of the invention and are not therefore to be consideredlimiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings, in which:

FIG. 1 is a block diagram of an embodiment of a vanadium redox batteryenergy storage system;

FIG. 2 is a block diagram illustrating an embodiment of a powerconversion system;

FIG. 3 is a block diagram of an embodiment of a control system;

FIG. 4 is a graph illustrating a state of charge curve;

FIG. 5 is graph illustrating a state of charge curve for ideal opencircuit voltages; and

FIG. 6 is a block diagram illustrating a control methodology for use inthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The presently preferred embodiments of the present invention will bebest understood by reference to the drawings, wherein like parts aredesignated by like numerals throughout. It will be readily understoodthat the components of the present invention, as generally described andillustrated in the figures herein, could be arranged and designed in awide variety of different configurations. Thus, the following moredetailed description of the embodiments of the apparatus, system, andmethod of the present invention, as represented in FIGS. 1 through 6, isnot intended to limit the scope of the invention, as claimed, but ismerely representative of presently preferred embodiments of theinvention.

A vanadium redox battery energy storage system, hereinafter referred toas VRB-ESS, includes all sizes of vanadium redox batteries (VRB) in bothabsolute KVA rating and energy storage duration in hours. The VRB-ESSincludes storage reservoirs to hold vanadium electrolyte, an energyconversion mechanism defined as a cell, a piping and pumping flowsystem, and a power conversion system (PCS).

The VRB-ESS is in electrical communication with a control system thatmonitors and controls aspects of the performance of the components ofthe VRB-ESS. The control system may be implemented in any number of waysbut, in one embodiment, includes a control program running on a suitableplatform, such as programmable logic controller, microprocessor, or thelike. The control system controls and manages the performance of theVRB-ESS in such a manner as to optimally meet the fundamental parametersof efficiency and safe operation. The control system further providesfor self protection in the event of an external or internal fault orfailure of a critical component, accurate controlled output asdetermined by dynamic load requirements or preset performancethresholds, and ambient conditions prevailing from time to time in eachcycle.

The present invention provides a system and method for optimallycontrolling the power output, charging and discharging times, andefficiency of a VRB-ESS or any system that uses vanadium basedelectrolyte solution as the energy storage component of a battery. Thereare several key parameters which control the operation of a VRB. For anygiven concentration of electrolyte solution, the key parameters includetemperature, volumetric flow rates, pressure within and across the cellstacks, and state of charge of the electrolyte and load as evidenced bythe current drawn or supplied. The load may be seen as positive ornegative. If negative, then the load is actually supplying power to theVRB. All of these parameters change in a dynamic manner continuously andvary with age.

In order to optimize the overall performance of the VRB, the presentinvention employs a control system provides algorithms with controlstrategies. The control system allows the VRB-ESS to operate in anautomatic mode to ensure that the highest possible efficiency isachieved as measured from the alternating current input to alternatingcurrent output on a round trip basis. The control system adjustsaccording to the age of the VRB-ESS or as dynamic changes in any of thecomponents occurs. The control system provides optimized efficiency bycontrolling the charging and discharging, pump flow rates, andassociated pressures within the VRB-ESS.

Referring to FIG. 1, a block diagram of a VRB-ESS 10 for use with thepresent invention is shown. A suitable energy storage system is requiredfor remote power system applications that are supplied by eitherphotovoltaic arrays or wind turbine generators. For such applications,low life-cycle cost and simplicity of operation are major requirements.

The system 10 includes one or more cells 12 that each have a negativecompartment 14 with a negative electrode 16 and a positive compartment18 with a positive electrode 20. Suitable electrodes include any numberof components known in the art and may include electrodes manufacturedin accordance with the teachings of U.S. Pat. No. 5,665,212, which ishereby incorporated by reference. The negative compartment 14 includesan anolyte solution 22 in electrical communication with the negativeelectrode 16. The anolyte solution 22 is an electrolyte containingspecified redox ions which are in a reduced state and are to be oxidizedduring the discharge process of a cell 12 or are in an oxidized stateand are to be reduced during the charging process of a cell 12 or whichare a mixture of these latter reduced ions and ions to be reduced. Thepositive compartment 18 contains a catholyte solution 24 in electricalcommunication with the positive electrode 20. The catholyte solution 24is an electrolyte containing specified redox ions which are in anoxidized state and are to be reduced during the discharge process of acell 12 or are in a reduced state and are to be oxidized during thecharging process of the cell 12 or which are a mixture of these oxidizedions and ions to be oxidized.

The anolyte and catholyte solutions 22, 24 may be prepared in accordancewith the teachings of U.S. Pat. Nos. 4,786,567, 6,143,443, 6,468,688,and 6,562,514, which are hereby incorporated by reference, or by othertechniques well known in the art. The anolyte solution 22 refers to anelectrolyte containing specified redox ions which are in a reduced stateand are to be oxidized during the discharge process of a redox batteryor are in an oxidized state and are to be reduced during the chargingprocess of a redox battery or which are a mixture of these latterreduced ions and ions to be reduced. The catholyte solution 24 refers toan electrolyte containing specified redox ions which are in an oxidizedstate and are to be reduced during the discharge process of a redoxbattery or are in a reduced state and are to be oxidized during thecharging process of the redox battery or which are a mixture of theseoxidized ions and ions to be oxidized. Further, aqueous NaOH is notincluded within the scope of anolyte solution 22, and aqueous HCl is notincluded within the scope of a catholyte solution 24. In one embodiment,the anolyte solution 22 is 1M to 6M H.sub.2 SO.sub.4 and includes astabilizing agent in an amount typically in the range of from 0.1 to 20wt % and the catholyte solution 24 is 1M to 6M H.sub.2 SO.sub.4.

Each cell 12 includes an ionically conducting separator 26 disposedbetween the positive and negative compartments 14, 18 and in contactwith the catholyte and anolyte solutions 22, 24 to provide ioniccommunication therebetween. The separator 26 serves as a proton exchangemembrane and may include a carbon material which may or may not bepurflomatorated.

Additional anolyte solution 22 is held in an anolyte reservoir 28 thatis in fluid communication with the negative compartment 14 through ananolyte supply line 30 and an anolyte return line 32. The anolytereservoir 28 may be embodied as a tank, bladder, or other containerknown in the art. The anolyte supply line 30 communicates with a pump 36and a heat exchanger 38. The pump 36 enables fluid movement of theanolyte solution 22 through the anolyte reservoir 28, supply line 30,negative compartment 14, and return line 32. The pump 36 has a variablespeed to allow variance in the generated flow rate. The heat exchanger38 transfers generated heat from the anolyte solution 22 to a fluid orgas medium. The pump 36 and heat exchanger 38 may be selected from anynumber of known, suitable devices.

The supply line 30 includes one or more supply line valves 40 to controlthe volumetric flow of anolyte solution. The return line 32 communicateswith a return line valves 44 that controls the return volumetric flow.

Similarly, additional catholyte solution 24 is held in a catholytereservoir 46 that is in fluid communication with the positivecompartment 18 through a catholyte supply line 48 and a catholyte returnline 50. The catholyte supply line 48 communicates with a pump 54 and aheat exchanger 56. A variable speed pump 54 enables flow of thecatholyte solution 22 through the catholyte reservoir 46, supply line48, positive compartment 18, and return line 50. The supply line 48includes a supply line valve 60 and the return line 50 includes a returnline valve 62.

The negative and positive electrodes 16, 20 are in electricalcommunication with a power source 64 and a load 66. A power sourceswitch 68 is disposed in series between the power source 64 and eachnegative electrode 16. Likewise, a load switch 70 is disposed in seriesbetween the load 66 and each negative electrode 16. One of skill in theart will appreciate that alternative circuit layouts are possible andthe embodiment of FIG. 1 is provided for illustrative purposes only.

In charging, the power source switch 68 is closed and the load switch isopened. Pump 36 pumps the anolyte solution 22 through the negativecompartment 14 and anolyte reservoir 28 via anolyte supply and returnlines 30, 32. Simultaneously, pump 54 pumps the catholyte solution 24through the positive compartment 18 and catholyte reservoir 46 viacatholyte supply and return lines 48, 50. Each cell 12 is charged bydelivering electrical energy from the power source 64 to negative andpositive electrodes 16, 20. The electrical energy derives divalentvanadium ions in the anolyte solution 22 and quinvalent vanadium ions inthe catholyte solution 24.

Electricity is drawn from each cell 12 by closing load switch 70 andopening power source switch 68. This causes load 66, which is inelectrical communication with negative and positive electrodes 16, 20 towithdraw electrical energy. Although not illustrated, a power conversionsystem may be incorporated to convert DC power to AC power as needed.

A number of control parameters influence the efficiency of the system10. A key control parameter is the temperature of the anolyte andcatholyte solutions 22, 24. The temperature is influenced by ambientconditions and load requirements. Another control parameter is thepressure of the solutions 22, 24 which is influenced by flow rates,state of charge (SOC), temperature, and plant design. A further controlparameter is the flow rate which is controlled through variable speeddrives. Other control parameters include charging current and durationof constant current periods, as determined by SOC.

Another control parameter is hydrogen evolution. The hydrogen evolutionis minimized in the control strategy and is influenced by temperature,SOC, load and rates of charge and discharge which are ramp rates.Another control parameter is the remixing of concentrations of theanolyte and catholyte solutions 22, 24 with respect to volumes. Pressuredifferentials develop over time as reservoirs 28, 46 have differentelectrolyte levels due to crossover. Concentrations also vary and systemoptimization must factor the remixing parameter.

Recharge and discharge periods are additional control parameters. Therate of charge and discharge impact the evolution of hydrogen. Inaddition, during discharge, heat is developed and the temperature of theanolyte and catholyte solutions 22, 24 is raised. Viscosity is thusaffected and pump flow rates need to be adjusted accordingly. Theoptimal time for charge and discharge is selected within the maximumrates that the system can handle as well as within the loadsrequirements, i.e. time available in a day.

Referring to FIG. 2, an interconnection of cells 12 of a VRB-ESS 10 to aPCS 100 is shown. The PCS 100 serves as the load 66 generally referencedin FIG. 1. The PCS 100 is illustrative of any number of configurationsand is provided as one example. One or more cells 12 are coupled to thePCS 100 through a load switch 70. The cells 12 provide a direct currentto a coupling circuit 102 that may include a capacitor 104 and diode 106in series. The coupling circuit 100 is in communication with an inverter108 to convert the direct current to alternating current. The inverter108 couples to a main switchboard 110 to provide local distribution.

One or more transformers 112, such as pole mount transformers, are inelectrical communication with the main switchboard 110 to step up thelocalized voltage for remote distribution. A distribution feeder 114 iscoupled to the transformer 112 to enable long range power transmission.

A panel board 116 is coupled to the main switchboard 110 for local powerdistribution. This is particularly useful if the system 10 is located ina remote location with limited power access. The panel board 116 is inelectrical communication with the pumps 36, 54 to power their operation.One or more power lines 118 are in communication with the panel board116 to provide high voltage supply to one or more applications such aslighting, HVAC, and so forth. A transformer 120, in electricalcommunication with the panel board 112, steps down the voltage for walloutlets and delivers the voltage to a sub panel 122. The sub panel 122is in electrical communication with one more wall outlets 124.

Referring to FIG. 3, a block diagram of one embodiment of a controlsystem 200 that interfaces with the system 10 of FIG. 1 is shown. Thecontrol system 200 may be embodied as a programmable logic computer witha processor 202 for executing applications of the present invention. Theprocessor 202 is in electrical communication with a memory 204 thatreceives and stores executable applications and data. The memory 204 maybe embodied in various ways and may collectively include differentmemory devices such as ROM, RAM, non-volatile memory, such as a magnetichard drive, and the like. The control system 200 further includes aninput 206 and an output 208 to enable user interaction.

A user enters control settings 210 into lookup tables 212 in the memory204. The control settings 210 include real time pricing requirements,anticipated demand peak limits, and projected charge and dischargeperiods for a VRB-ESS 10.

The control system 200 is in communication with the various componentsof the system 10 through a control communications interface 214, thatmay be embodied as a RS485 using a MODBUS protocol. The components inelectrical communication with the control system 200 include pumps 36,54, heat exchangers 38, 56, supply valves 40, 60, return valves 44, 62,power source switch 68, and load switch 70. The control system 200further communicates with an equalization/mix control 215 that equalizesthe anolyte and catholyte solutions 22, 24 in the reservoirs 28, 46. Asrequired, the equalization/mix control 215 increases or decreases thevolume of electrolytes in the reservoirs 28, 46 to maintain approximateequalization of anolyte and catholyte solutions 22, 24. Theequalization/mix control 215 may provide additional anolyte andcatholyte solution 22, 24 from auxiliary reservoirs (not show) or reducesolution 22, 24 through drains (not shown).

The control system 200 communicates with sensors 216 through a monitorcommunications interface 218 that may be similar to the controlcommunications interface 214. The sensors 216 are disposed within thesystem 10 to monitor performance. The sensors 216 may include anolyteand catholyte thermometers 220 a, 220 b to monitor electrolytetemperatures. The anolyte and catholyte thermometers 220 a, 220 b are incontact with the anolyte and catholyte solutions 22, 24 and may bedisposed at any number of locations throughout the VRB-ESS 10. Thesensors 216 further include an ambient thermometer 222 to monitor theexternal ambient temperature. Electrolyte level sensors 224 a, 224 b aredisposed in the anolyte reservoir 28 and the catholyte reservoir 46respectively to monitor levels of anolyte and catholyte solutions 22,24. Anolyte and catholyte flow rate sensors 226 a, 226 b are disposed inthe supply and/or return lines 30, 32, 48, 50 to measure volumetric flowrate of the anolyte and catholyte solutions 22, 24. Anolyte andcatholyte pressure sensors 228 a, 228 b are disposed in the system 10 tomeasure the pressure of the anolyte and catholyte solutions 22, 24 inthe supply and/or return lines 30, 32, 48, 50. One or more emissionsensors 230 are disposed in the system 10 to monitor the quantity of H2emissions generated by the cells.

The communications interface 218 is further in electrical communicationwith the cells 12 to determine the Voc (open-circuit voltage) or to areference cell inside the cell stack 12 of the system 10. Thecommunications interface 218 is also in electrical communication withthe PCS 100 to receive signals indicative of voltage and currentdelivered to and received from the PCS 100. All sensor input iscollectively referred to as operational data 228 which is relayed to thecontrol system 200 and stored in the memory 204.

The control system 200 includes a control module 232, resident in memory204, that controls and monitors system performance. The control module232 monitors the operational data 228 for enhancements and determinationof changes in performance. The control module 232 is an algorithmicapplication that evaluates the dynamic conditions of the system 10 byreviewing the operational data 228 and adjusts the control variables ofsystem components to maximize the efficiency within the given designrequirements. The control module 232 takes into account the effects ofhysterisis and lag times in terms of response.

In operation, meeting grid demands is a dynamic situation. As loadincreases, the control system 200 meets the demand by increasing pumpspeeds to supply more power. Accordingly, as load decreases, the pumpspeeds are decreased. Furthermore, the more charge in the electrolytesolution, the slower the pump speed to meet a demand. Conversely, theless charge in an electrolyte solution, the faster the pump speed tomeet a demand. In charging a VRB, the less charge in the electrolyte,the slower the pump speed needed to charge the electrolyte, whereas thegreater charge in the electrolyte the faster the pump speed needed tocharge the electrolyte. Furthermore, different pump speeds are employedbased on the different types of electrolytes and concentrations.

The control module 232 employs the following control strategy equation:

SOC=(A+B*Voc ^(C))/(D+Voc ^(C)),

where SOC is the state-of-charge and Voc is the open-circuit voltage. A,B, C, and D are constants. The control strategy equation defines afundamental relationship between Voc and the SOC. Referring to FIG. 4, agraph is shown illustrating one example of the shape of a plot of Voc asa function of SOC. Referring to FIG. 5, a graph illustrating an idealVoc as a function of SOC is shown. The relationship may also beconfirmed against a reference cell.

The variables, A, B, C, and D are determined by physical design factorssuch as the pressure of cell stacks, ambient temperature, internaltemperature, length of pipes, molar concentrations of electrolyte, andother design and operating factors. Although the plot shown in FIG. 4may vary and shift based on variables, the fundamental curve shaperemains. The control module 232 uses the above equation to calculate theSOC based upon the open-circuit voltage Voc. A unique consideration ofthe present invention is that not all variables need to be activelycontrolled. Some variables are dependent upon others with definite timelags total system 10 operates as a feedback mechanism.

The flow rates of the anolyte and catholyte solutions 22, 24 may bevaried to affect the Voc, SOC, and, consequently, power output. Thecontrol system 200 operates the pumps 36, 54 and heat exchangers 38, 56to vary pump speeds and temperature and control the flow rate in thesupply and return lines 30, 32, 48, 50. The control system 200 cancontrol flow rates to yield a constant power output, a constant currentor a constant voltage. The control module 232 monitors the generated Vocand SOC to determine if the system 10 is performing efficiently. Ifperformance is below expectations, the control module 232 alters keyparameters of pump speed and temperature to improve performance. In thismanner, the control module 232 adapts and improves control of the system10.

In discharging the system 10, the control system 200 operates the pumps36, 54 and heat exchangers 38, 56 to adjust the flow rate to optimizeefficiencies and available power. With SOC at higher states and whendischarging, the anolyte and catholyte solutions 22, 24 are pumpedslower so that more charge can be removed on each pass. With SOC atlower states and when discharging, the pumping speeds are increased tothe maximum allowable under pressure rating limits.

As the anolyte and catholyte solutions 22, 24 discharge, they becomemore viscous so flow rates can increase without equivalent pressurebuild up. To extract more power down to 10 percent SOC, it is necessaryto increase the flow rate. When discharging, there is an exothermicreaction when the anolyte and catholyte solution 22, 24 states change.This typically results in a rising temperature of the electrolyte,unevenly from positive to negative sides. Temperature limits aretypically set at a minimum of 5 Celsius and at a maximum of 40 Celsius.The control system 200 determines lead and lag times associated witheach charge/discharge cycle and establishes set points. The set pointsdetermine when the control system 200 operates the heat exchangers 38,56 to extract heat from the anolyte and catholyte solutions 22, 24.Ambient conditions impact this process so that the condition iscontinuously dynamic.

During charging of the system 10, the control system 200 controls thepumping speed at the extremes of the SOC in order to optimize the powerinput and output and to enhance round trip efficiency. With SOC athigher states and when charging, faster pumping prevents chargedelectrolyte from being trapped and developing heat and gas emission andpotentially V₂O₅. With SOC at lower states and when charging, slowerpumping allows maximum energy transfer each pass to reduce gas emission.

By use of emission sensors 230, the control system 200 monitors anyhydrogen gas evolution under bad conditions within each cell 12 duringthe charging process. In general, H₂ gas evolves during the chargingcycle. Gas evolution is generally higher at a higher SOC and the controlsystem determines the optimal performance criteria. If excess H₂ isproduced, the efficiency drops off. During charging, the temperatures ofthe anolyte and catholyte solutions 22, 24 do not rise and may declinedepending upon starting points and rates of charge.

Referring to FIG. 6, a block diagram illustrating a specific controlmethodology 300 performed by the control module 232 is shown. In a firstprocess, the control module calculates 302 the SOC of the system 10. Inthe previously discussed equation, SOC is calculated from the Voc of thecells 12 or reference cell.

Next the control module 232 calculates 304 the dynamic pumping speed foreach pump 36, 54. Pumping speed is determined by the calculated 302 SOC,and anolyte and catholyte pressures. Furthermore, pumping speed isadjusted by the calculated 312 charge and discharge rates, calculated310 system efficiency, and cell H2 emissions. The optimal pumping speedsare transmitted from the control system 200 to each pump 36, 54.

The control module 232 further calculates 306 an optimal temperaturerange for the anolyte and catholyte solutions 22, 24 based on thecalculated 302 SOC and calculated 304 pumping speeds. The control module232 operates the heat exchangers 38, 56 in accordance with the ambientand electrolyte temperature range. During charge and discharge, heat isgenerated and is measured to maintain an optimal range. As needed, heatis removed to maintain an optimal temperature range. In sufficientlycold environments, no heat exchangers are required as the ambient airprovides the needed cooling.

During operation, the control module 232 monitors the levels of theanolyte and catholyte solutions 22, 24 and determines 308 ifequalization of reservoir levels is needed. The control module 232operates the equalization/mix control 215 to adjust the reservoirs 28,46 as needed.

The control module 232 calculates 310 system efficiency based on a ratioof power output versus power input. System efficiency is determined fromvoltage and current generated by the cells 12, calculated 314 powerfactor, and voltage and current delivered to the PCS 100. Systemefficiency is used in calculating 304 the pump speeds.

The control module 232 accesses the control settings 210 to retrieveavailable charge and discharge periods. The control module 232 thencalculates 312 charge and discharge rates to minimize demand peaks andto optimize efficiency. The charge and discharge rates are calculatedinitially and then may be updated and calculated under dynamic demandconditions. The charge and discharge rates are used in calculating 304the pump speeds.

The control module 232 calculates 314 a power factor based on voltageand current received and delivered to and from the PCS 100. The controlmodule 232 further calculates 314 the optimal charge and discharge ratesbased on the calculated 312 charge and discharge rates. The controlmodule 232 may modify the projected charge and discharge rates based onprior rates. The control module 232 may communicate the charge anddischarge rates to the PCS 100 for anticipated performance.

In operation, meeting grid demands is a dynamic situation. As loadincreases, the PCS 100 meets the demand by increasing pump speeds tosupply more power depending on the SOC. Accordingly, as load decreases,the pump speeds are decreased. Furthermore, the more charge in theelectrolyte solution, the slower the pump speed to meet a demand.Conversely, the less charge in an electrolyte solution, the faster thepump speed to meet a demand. In charging a VRB, the less charge in theelectrolyte, the slower the pump speed needed to charge the electrolyte,whereas the greater charge in the electrolyte the faster the pump speedneeded to charge the electrolyte.

The processes disclosed in the methodology 300 frequently operate inparallel and, as illustrated, interrelate with one another. The system'sdynamic conditions require constant monitoring of system variables, suchas Voc, pressure, temperature, and so forth. The control module 232continuously updates the pump speeds, electrolyte temperatures, andreservoir levels to optimize performance. The control module 232 may beimplemented in various ways including a neural networks or more simplywith standard logic programming.

It will be obvious to those having skill in the art that many changesmay be made to the details of the above-described embodiments withoutdeparting from the underlying principles of the invention. The scope ofthe present invention should, therefore, be determined only by thefollowing claims.

1. A computer implemented method for controlling a vanadium redoxbattery energy storage system configured to couple to an electrical gridand operate responsive to the conditions of the electrical grid,comprising: receiving signals indicative of an open-circuit voltage of avanadium redox battery cell of the vanadium redox battery energy storagesystem; receiving anolyte and catholyte solution temperature signalsfrom the vanadium redox battery energy storage system; calculating astate-of-charge for the vanadium redox battery cell based on theopen-circuit voltage and anolyte and catholyte solution temperaturesignals; calculating charge and discharge rates of the vanadium redoxbattery energy storage system; calculating anolyte and catholyte pumpspeeds based on the state-of-charge, the charge and discharge rates, andgrid conditions; and generating anolyte and catholyte pump speed signalsto transmit to the vanadium redox battery energy storage system tocontrol anolyte and catholyte pump speeds.
 2. The method of claim 1,further comprising: receiving anolyte and catholyte pressure signalsfrom the vanadium redox battery energy storage system, and whereincalculating anolyte and catholyte pump speeds is further determined bythe anolyte and catholyte pressure signals.
 3. The method of claim 1,further comprising: calculating an anolyte temperature range and acatholyte temperature range based on the state-of-charge and the anolyteand catholyte pump speeds; and generating anolyte and catholytetemperature ranges to transmit to the vanadium redox battery energystorage system.
 4. The method of claim 1, further comprising: receivingan ambient temperature signal, and wherein calculating thestate-of-charge is further determined by the ambient temperature signal.5. The method of claim 1, further comprising: receiving a hydrogenemission signal indicative of a quantity of hydrogen emissions generatedby the vanadium redox battery energy storage system, and whereincalculating anolyte and catholyte pump speeds is further determined bythe quantity of hydrogen emissions.
 6. The method of claim 1, furthercomprising calculating optimal charge and discharge rates derived fromthe charge and discharge rates.
 7. The method of claim 1, furthercomprising: calculating a system efficiency for the vanadium redoxbattery energy storage system, and wherein calculating anolyte andcatholyte pump speeds is further determined by the system efficiency. 8.The method of claim 1, further comprising: receiving anolyte andcatholyte reservoir level signals; and determining if equalization ofthe anolyte reservoir and catholyte reservoir is required.
 9. The methodof claim 1, further comprising calculating a power factor derived frominput voltage and input current to the vanadium redox battery energystorage system and output voltage and output current from the vanadiumredox battery energy storage system.
 10. A non-transitory computerreadable storage medium having stored thereon computer executableinstructions for performing a method for controlling a vanadium redoxbattery energy storage system configured to couple to an electrical gridand operate responsive to the conditions of the electrical grid, themethod comprising: receiving signals indicative of an open-circuitvoltage of a vanadium redox battery cell of the vanadium redox batteryenergy storage system; receiving anolyte and catholyte solutiontemperature signals from the vanadium redox battery energy storagesystem; calculating a state-of-charge for the vanadium redox batterycell based on the open-circuit voltage and anolyte and catholytesolution temperature signals; calculating charge and discharge rates ofthe vanadium redox battery energy storage system; calculating anolyteand catholyte pump speeds based on the state-of-charge, the charge anddischarge rates, and grid conditions; and generating anolyte andcatholyte pump speed signals to transmit to the vanadium redox batteryenergy storage system to control anolyte and catholyte pump speeds. 11.The computer readable medium of claim 10, wherein the method furthercomprises: receiving anolyte and catholyte pressure signals from thevanadium redox battery energy storage system, and wherein calculatinganolyte and catholyte pump speeds is further determined by the anolyteand catholyte pressure signals.
 12. The computer readable medium ofclaim 10, wherein the method further comprises: calculating an anolytetemperature range and a catholyte temperature range based on thestate-of-charge and the anolyte and catholyte pump speeds; andtransmitting the anolyte and catholyte temperature ranges to thevanadium redox battery energy storage system
 13. The computer readablemedium of claim 10, wherein the method further comprises: receiving anambient temperature signal; and wherein calculating the state-of-chargeis further determined by the ambient temperature signal.
 14. Thecomputer readable medium of claim 10, wherein the method furthercomprises: receiving a hydrogen emission signal indicative of a quantityof hydrogen emissions generated by the vanadium redox battery energystorage system; and wherein calculating anolyte and catholyte pumpspeeds is further determined by the quantity of hydrogen emissions. 15.The computer readable medium of claim 10, wherein the method furthercomprises calculating optimal charge and discharge rates derived fromthe charge and discharge rates.
 16. The computer readable medium ofclaim 10, wherein the method further comprises: calculating a systemefficiency for the vanadium redox battery energy storage system; andwherein calculating anolyte and catholyte pump speeds is furtherdetermined by the system efficiency.
 17. The computer readable medium ofclaim 10, wherein the method further comprises: receiving anolyte andcatholyte reservoir level signals; and determining if equalization ofthe anolyte reservoir and catholyte reservoir is required.
 18. Thecomputer readable medium of claim 10, wherein the method furthercomprises calculating a power factor derived from an input voltage andan input current to the vanadium redox battery energy storage system andan output voltage and an output current from the vanadium redox batteryenergy storage system.